Played cards become discarded after being resolved just as the cards discarded for other reasons.

That is exactly how you use Reload - play your red card first, then play reload, then use your red card again.

And don't forget that you still only play one card per turn so if you reload on turn 2 you don't get to use the red card immediately. It goes to your hand first and you play it in any subsequent turn.Hence, using Reload as a skill becomes pointless on Turn 4, since you won't be able to use the retrieved card anyway)

There's a theory: if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There's another theory: this has already happened.

And tying in with the other thread, I guess this will also let her retrieve the red card discarded for turn 1 after she has been killed and respawned.

The barbarian also has a card that lets one of their allies take back a discarded card into their hand. Does it mean that even a played card can be taken back ?

Yep.

Card in hand -> Played -> Discarded (and placed on the curren Turn slot of the mat)Card in hand -> Use Defence (re)action -> Discarded (and placed on the side of the mat)Card in hand -> Some effect which forces you to discard a card -> Discarded (and placed on the side of the mat)Hero defeated -> All cards are returned to player's hand, red card Discarded (and placed on Turn 1 slot of the mat).